ANGIOTENSIN-II BINDING-SITES IN FROG KIDNEY AND ADRENAL

Angiotensin II (AII) binding sites were localized and quantified in kidney and adrenal of the frog Rana temporaria by quantitative in vitro autoradiography. AII binding was present in kidney glomeruli and in interrenal tissue of the outer zone of the adrenal gland. Saturation experiments showed that [I-125]-[Val5]AII binds to a single class of binding sites with a dissociation constant (K(d)) of 548 +/- 125 pM in glomeruli and 593 +/- 185 pM in interrenal tissue (n = 8). The corresponding maximal binding capacities (B(max)) were 2.48 +/- 0.71 and 3.05 +/- 1.02 fmol/mm2, respectively. All binding was displaced by unlabeled angiotensin analogues in the rank order: [Sar1]AII > human AII > [I-125]-[Val5]AII = [Val5]AII = human AIII > > human AI. The AII binding sites in glomeruli and interrenal tissue suggest an influence of AII on glomerular filtration rate and adrenal steroid secretion to take part in osmomineral regulation of the frog.